Electronic switching apparatus



May 25, 1954 w. HURFORD ELECTRONIC SWITCHING APPARATUS 4 sheets-sheet 1 Filed May 31, 1950 @muni-.mw

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WZOFFD@ IWDL ce Inventor: WinSlw l.. Huhford, b M y His Att May 25, 1954 -w. L. HURFORD y ELECTRONIC SWITCHING APPARATUS 4 Sheets-Sheet 42 Filed May 31,' 1950 J r Inventor:-

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May 25, 1954 w. L. HuRFoRD ELECTRONIC SWITCHING APPARATUS 4 Sheets-Sheet 3 Filed May 5l, 1950 TIME- TIME` Inventor* Winslow L. Hurord by fm 7mm His Attorney.

May 25, 1954 w, L. Hum-ORD I ELECTRONIC SWITCHING APPARATUS 4 Sheets-Sheet 4 Filed May 5l, 1950 |1||| B VI l .m y :o e r n H. H. tH n @n @L M vw In@ S .mm W Y .D

4ing a smooth transition from Patented May 25, 1954 UNITED YSTATES PATENT OFFICE .2,679,554 yEI-EL*IRONIC SWITCHING APPARATUS Winslow L. Hurford, North Syracuse, N. Y., as-

signor to General Electric ration of New Yor Company, Pa corpo- 4 Claims.

1 The present invention yrelates to electrical switching apparatus and has :particular application to the 'television arts where it .is desired to ei'ect a transition `from one televised picture to on the receiver second picture builds up be sharply defined and lbe maintained essentially the same.

Accordingly, it is an important object. of :my invention to provide improved means for effectone television picture to another.

An exemplary embodiment of -my invention comprises two signal ampliers vhaving a vcommon plate load impedance. The gain of each amplier is ycontrolled by resistance-capacitance networks having diode level setters connected in the grid circuit of -each amplifier. Normally `one amplifier is conducting and the other is :nonconvductive. By'actuation of a switch onenetwork Vis permitted to discharge while .permitted to charge so that the amplier that was on is now off and vice versa. The diode level Setters-set the value to which :the capacitors in the 'network charge. By appropriately choosing .the value to which the capacitors discharge a fade -or a lap dissolve may be achieved. By a fade is meant a transition in which the first :picture decays `or dissolves to vsubstantial zero light level before the second picturestarts to build up. By a, lap .is meant a transition in which the second .picture starts to build up before the rst picture has completely decayed.

Accordingly, it is also an important object of my vinvention to provide means `for producing a lap or a fade `between pictures on a televisionscreen.

A general object of .my invention is to .provide improvements inelectrical .switching circuits.

The novel vfeatures which I Vbelieve to be characteristic of my invention-are set forth with particu-larity in the appended claims. Myinvention itself, however, .both `as to its organization and method of operation together with further obljects and advantages .thereof may vbest be understood by reference to the .following description the other network is tak-en in connection with the accompanying drawings in which Fig. 1 shows -a block :diagram of a system embodying my invention; Fig. 2 shows that c'portion yof the detailed circuits of `the system fofFig. 1 comprising the .channel ampliers, the D.C.. level -setters and ,the vlap-fade control unit; Fig. 3A is a diagram :showing the manner .in which the gain of one channel .ampliiier is permited. to decay from a predetermined level .while `'at the same .time the gain :of-another-.channel amplifier iis permitted to .build .up to .a .predetermined level or value; Fig. `3B is a diagram showing another way in which :the .gain of one Achannel amplifier .is permitted to .decrease `from l .a predetermined value `while at the .same .time

the ,gain of another channel .amplier is permitted to .increase to a predetermined value; Eig. .4 shows the circuitdetails .ofthe .remaining elements .shown ,in block .form :in Fig. T1.

Referring .now to lFig. '1, there .is shown va 'block .diagram of .a system embodying my invention. The .system .comprises .a group of `channel .am-

'rhe 'lap-fade control unit 's and .active .in permitting .the passage of ia .signal .on

'Ifhefremaining channel .am- .pliners areheld ;cut oil Iley Athe lap-fade fcontrol -unit 6. To effect -a transition from .one picture .to another :a ,push-button in vthe lap-fade `control Iunit :for examplepush-button .60, shown .in the lower left-hand corner 'fof Fig. il, .is .depressed te cause the amplier that was previously conductive to become nonconductive and -to cause ythe amplifier rassociated `with the push-.button depressed to become conductive .to `pass .thesec- .ond .picture signal. -ilhe manner .in which .this 4latter function is .achieved will v,become .apparent vfrom a consideration of Athe `detailed circuits shown Ain .2.

The 'remaining portions 4on the lblock vv.diagram .show `elements for v'amplifying :the .video .signal from .the channel lamplifiers..and for suitably handling the `signal -so .that .it can .be fed into other studio :equipment prior to Vtransmission over the a-ir. Video lamplifiers .8 .and v9 .amplify the video vsign-al obtained from .the .channel amplifiers. .synchronizing .signal :mixer .lil .performs .the :function of mixing -the .synchronizing .th-rough the system.

van anode, a cathode and a grid.

point upon voltage divider 24.

is connected to.

signals with the video signal to form the television signal. The keyed clamp I I and the clamp keyer I2 perform the function of reinserting the proper unidirectional component into the signal coming from the video amplifier 9. The video signal from the video amplifier 9 with the proper D.C. insertion and with the synchronizing signals is fed into a cathode follower I3 which feeds an impedance adjusting stage I4. The impedance adjusting stage is for the purpose of adl justing the impedance at the driving point of an output line to the impedance presented by the line.

Referring now to Fig. 2 there is shown a schematic diagram of a portion of the block diagram of Fig. l comprising the channel amplifiers I, 2, 3, Il and 5, the lap-fad@l control unit 5 and theA D.C. level setters 1. The manner of operation of the circuit will best be understood by focusing Aattention on the operation of two channel amplifiers, for example, channel amplifiers 2 and 3, during the switching operation. Channel amplider 2 comprises a dual -triode type of electron discharge device I5, each triode section having The cathodes I6 and I1 are connected together and are also connected to ground through resistances I8 and I9. The grid 29 of the left-hand section of electron discharge device I5 is connected to a source of video signal through a coupling capacitor 2| and a voltage divider 22. The grid 20 is also connected through a grid resistor 13 to a positive The plate or anode is connected to B+ potental. The grid 26 of the right-hand section of electron discharge device I5 is connected through a diode or rectifying element 21 to the same positive potential on the voltage divider 24 that the grid 20 of the left-hand section of electron discharge device I5 The plate of the diode 21 is connected to the grid 26 and the cathode of the diode 21 is connected to the voltage divider 24. The grid 26 is also connected to a voltage divider comprising resistances 28 and 29 which are connected to a source of B+ potential through resistance 33. One end of capacitor 39 is connected 4to ground and the other end of capacitor 30 is connected through a switch 32 and a resistance 33 to the same source or" B+ potential. y The circuit connections of channel amplifier 3 '50 are similar to the circuit connections of channel amplifier 2. The anodes or plates 34 and 35 of electron discharge devices I5 and 36 are connected through a common plate load impedance 31 to a source of B+ potential. observed that switch 32 is associated with the -circuits of channel amplifier 2 and that switch 38 is associated with the circuits of channel amplifier 3. Since the switch 33 is not depressed, the grid side of capacitor 39 is connected throughv a switch 38 and discharge resistor 40 to a positive point on voltage divider 24.

In the general operation of the system only `vone channel amplifier is passing a signal just before the transition period when it is desired-.'55

to change from one scene or picture to another. With switch 32 depressed and with switch 38 up, channel amplifier 2 would be conducting and channel amplifier 3 would be cut off, that is, the

signal coming into channel amplifier 2 would-A 70 vbe permitted to pass through while the signal coming into channel amplifier 3 would be blocked. With switch 32 in the down position grid 260i electron discharge device I5 is connected to a source of B+ potential through voltage divider* It should be The potential applied to the grid is limited by means of the switch 38 in the up positiongrid 4I vofchannel amplier 3 is connected to a potential point on voltage divider 24 which is less positive than the potential applied to grid 26 by an amount sumcient to render channel amplifier 3 nonconducting to any video signal appearing at the input grid 46 of `channel amplifier 3.

When a channel amplifier is conductive to a video signal applied to its input terminals both sections of the amplifier pass current. When a channel amplifier is non-conductive to a video signal applied to its input terminal only the left section passes current. Accordingly a higher cathode resistance is needed in the latter case to supply sufficient bias potential to the right section to maintain it cut off. With switch 32 down resistance I9 is shorted out of the circuit 'of channel amplifier 2. With switch 38 up reother the switch associated withthe corresponding amplifier to which the desired signal is applied is depressed. This causes the switch section of the amplifier that has previously been passing a signal to assume its up position. Let us suppose that the switch section 38 of channel ain- `plifier 3 has been depressed causing the switch section 32 of channel amplifier 2 to assume its up position. It will be recalled that channel amplifier 2 has been amplifying a signal which has appeared across load impedance 31 common to all the channel amplifiers. When the switch section 32 of channel amplifier 2 is in the up position the capacitor 30 which has been charged to essentially B+ potential starts to discharge through resistance 41l to a point which is below ually decrease to a value sufcient to cut the channel amplifier 2 off. This operation is assisted by switching cathode resistance I9 into the circuit when the switch 32 is in the up position. Channel amplier 2 now is in the nonconductive condition that channel amplifier 3 was in before the 'push-button associated with switch 38 was depressed.

While the signal coming through channel amplifler 2 has progressively decreased the signal coming through channel amplifier 3 has steadily increased to the same level from which the signal from channel amplifier 2 has decreased. The manner in which this was donewill be apparent from the following considerations. The depressing of switch 38 of thechannel amplifier 3 connected the capacitor 39 through a charging resistance 33 to B+ potential. A charging of capacitor 39 caused a rise in the potential at the grid 4I of the right-hand section of channel amplifiei` 3 at a rate determined by the time constant Acomprising principally capacitor 39 and resistance 33. The positive potential on grid 4I is not allowed to increase indefinitely but is heldto a predetermined value by means of the diode level 75.setter 42, one end of which is connected to the grid the other end is connected to a predetervoltage divider 24. The diode level setter d2 may be any suitable rectier device which presents a low impedance to voltagesy of one polarity and a high the opposite polarity impedance to voltages of applied to its terminals.

charge device i5 to ground and at the same time capacitor 39 is removed from the grid circuit by switch 641 the potential of grid 26 drops abruptly to render channel amplier 2 abruptly nonconductive. Curve 52 represents the voltage on the The rate of build up of grid potential in channel amplifier 3 may be changed by connecting a different resistance t? in the charging circuit by means of switch BS. the grid circuit directly to B+ and at the same time capacitor 39 is removed from the grid circuit by means of switch t6, the potential of grid lll rises abruptly to render channel amplier 3 abruptly conductive. The charging characteristics ofthe other channel ampliiers may be similarly changed. The lower level 53 of the voltage to which the grid of right section of channel amplier 2 drops is determined by the value to which the capacitor 3? is discharged and particularly is determined by. the point 54 on the vol*- age divider 2li to which capacitor Sil is connected through switch 55. The dotted portion of curve 52 represents the Way in which the voltage would rise on grid di in a circuit not having a diode level setter. The dotted ordinate 55 represents the value or grid potential at which the amplifiers are cut ofi, that is, become nonconductive or blocked. Potential points 5i; are chosen to form ;he picture coming through vill fade dissolve from a full value to zero at When switch 68 connects 39 is disthe grid circuit Fig. 3B there are shown grid voltage as a function of time for a lap picture effect. The picture eiiect in which one picture is permitted to build up before the other has completely faded is called lap The upper level to which the grid pctontial ci is permitted to rise is de- 1e cutoi potential of ampliers is represented by the respect to the cutoff bias 5.3.

Channel ampliers i, Il, and 5 identical to channel ampliers are substantially 2 and 3. By deagian particular channel is on the air. The connections 'I3 go to remote locations, for instance to studio cameras to indicate at that point when a particular program is being televised.

Referring now to Fig. 4 there are shown circuit elements of applicants system which are entirely conventional and it is believed that their function will be apparent upon inspection without detailed explanation. These elements which are set forth in blocked diagram in Fig. 1 comprise amplifiers 8 and 9, the synchronizing signal mixer I0, the keyed clamp Il, the cathode follower I3 and the impedance adjusting stage i4. The video signal coming from the channel amplifiers is fed into the video amplifiers 8 and 9. Since the unidirectional component of the video signal supplied to the channel amplifiers is removed by the video amplifiers a keyed clamp ii is used to reinsert the unidirectional component. The clamp l l is keyed by synchronizing signals fed into the clamp keyer l2. The keyed clamp H and clamp keyer I2 are of the kind disclosed in U. S. Patents Nos. 2,299,945 and 2,313,906 and further disclosed in an article by K. R. Wendt in R. C. A. Review, March 1948. The synchronizing signal is suitably mixed with the vdeo signal from the video amplifier by the synchronizing signal mixer l0 before the clamping operation is effected. The video signal with the synchronizing signal and the proper D.-C. reinsertion is fed into a cathode follower i3 prior to being ap lied to an impedance adjusting stage I4 and prior to being supplied to a transmitter for broadcast purposes.

While I have shown a particular embodiment of my invention, it will of course be understood that I do not wish to be limited thereto since many modifications, both in the circuit arrangement and in the instrumentalities employed may be made and I therefore contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a pair of electron discharge amplifiers each having a grid, a cathode, and an anode, a cathode resistor connecting each said cathode to ground, individual signal sources connected between the grids of respective amplifiers and ground, an output circuit connected between the anode of each of said amplifiers and ground, and means to vary the bias of said amphfiers in opposite senses to render them alternately operative, said bias varying means comprising a pair of unilaterally conductive devices, each connected between the grid of a respective one of said amplifiers and a point of reference potential,

said devices each being poled to be non-conductive when the voltage at said grid is below said reference potential and to be conductive when said voltage at said grid exceeds said reference potential, a pair of capacitors, one connected between the grid of each amplifier and ground and `means simultaneously to charge either capacitor to cause conduction of the respective unilaterally conductive device thereby to render the corresponding amplifier operative and to discharge the other of said capacitors to render the corresponding amplifier non-operative, the magnitude of said reference potential being selectedv in relation to the voltage variations on said capacitor due to the charging thereof so that the voltage-time characteristic variations impressed on said grid as their values approach the maximum value determined by the corresponding reference potential and unilaterally conductive device are substantially linear.

2. In combination, a pair of electron discharge amplifiers each having a grid, a cathode, and an anode, a cathode resistor connecting each said cathode to ground, individual signal sources connected between the grid of respective amplifiers and ground, an output circuit connected between the anode of each of said amplifiers and ground, and means to vary the gain of said amplifiers in opposite senses in a manner to render them alternately operative, said gain varying means comprising a pair` of unilaterally conductive devices, each connected between the grid of a respective one of said amplifiers and a point of reference potential, each of said devices being poled to be non-conductive when the voltage at said grid is below said reference potential and to be conductive when said voltage at said grid exceeds said reference potential, said reference potential corresponding to a predetermined gain of each of said amplifiers, a pair of capacitors each shunted by a resistance, a portion o one resistance being connected between the grid of one of said amplifiers and ground, a portion of the other resistance being connected between the grid of the other of said amplifiers and ground, and means simultaneously to charge either capacitor to cause conduction of the respective unilaterally conducting device and thereby to render said corresponding ampliiler operative and to discharge the other of said capacitors to render the corresponding amplifier non-conductive, the magnitude of said reerence potential being selected in relation to the voltage variations on said capacitor due to the charging thereof so that the voltage-time characteristic variations impressed on said grid as their values approach the maximum value determined by the corresponding reference potential and unilaterally conductive device are substantially linear.

3. In combination, a pair of electron discharge amplifiers each having a grid, a cathode, and an anode, a cathode resistor connecting each said cathode to ground, individual signal sources connected between the grid of respective amplifiers and ground, an output circuit connected between the anode oi each of said amplifiers and ground, a pair of unilaterally conductive devices, each connected between the grid of a respective one of said amplifiers and a point of reference potential, each of said devices being poled to be conductive when the voltage at said grid exceeds said reference potential and to be nonconductivewhen the voltage on said grid is below said reference potential a pair o capacitors, one connected between the grid of each amplifier and ground, and means simultaneously to charge either capacitor at a predetermined rate to a. voltage above said reference potential thereby to cause conduction of the respective unilaterally conductive devices thereby to increase the galli of said amplifier at said predetermined rate to a maximum value determined by the magnitude of said reference potential and simultaneously to discharge the other of said capacitors, the magnitude of said reference p0- tential being selected in relation to the voltage variations on said capacitor due to the charging thereof so that the voltage-time characteristic variations impressed on said grid as their value:

`approach the maximum value determined by thi corresponding reference potential and unilateral 75 ly conductive device are substantially linear,

UNITED STATES PATENTS References Cid in the le of this patent Number Name Date Konkle May 18, 1937 Konkle Feb. 25, 1941 Schnitzer Apr. 29, 1941 Miller, Jr Dec. 10, 1946 Holland et al. Jan. 27, 1948 Ussler, Jr. Dec. 6, 1949 Duke July 25, 1950 Brown, Jr. Sept. 12, 1950 Smeltzer Dec. 26, 1950 White et al. Dec. 26, 1950 Glasford Mar. 27, 1951 `Mofett Sept. 9, 1952 

